1. Field of the Invention
The present invention relates to a lithographic apparatus, a method of manufacturing a device, and a method of performing maintenance.
2. Brief Description of Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that circumstance, a patterning device, such as a mask, may be used to generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. comprising part of, one or several dies) on a substrate (e.g. a silicon wafer) that has a layer of radiation-sensitive material (resist). In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion in one go, and so-called scanners, in which each target portion is irradiated by scanning the pattern through the projection beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction.
Some types of lithographic apparatuses, such as those using an electron beam or an ion beam, have to be operated in a vacuum environment. For instance, lithographic apparatuses projecting electromagnetic radiation in the Extreme Ultraviolet (EUV) range require a vacuum, inter alia because gas molecules absorb this type of radiation and because hydrocarbons and water react under the influence of EUV radiation and contaminate the lithographic apparatus. To prevent these deterring effects, it is known to provide a vacuum system comprising a single vacuum chamber in which a lithographic apparatus is positioned. The vacuum chamber is connected to a vacuum pump system and can be pumped to a level of vacuum to operate the lithographic apparatus.
However, a draw-back of this prior art solution is that there is a high risk of contamination of the vacuum system, because different parts of the lithographic apparatus are handled and touched during assembly and maintenance of the lithographic apparatus. Each of those parts can become contaminated, for example with grease, dust, or otherwise. If the contaminated parts are positioned in the vacuum, they can release gases and other contaminants. Accordingly, the level of vacuum to operate the lithographic apparatus can not be obtained.
From the U.S. Pat. No. 6,333,775, a photolithographic apparatus is known. The apparatus includes a housing defining a vacuum chamber. Trays are situated in the vacuum chamber, which separate the vacuum chamber into compartments which are at different pressures. The tray is supported by a support member, and adjoined to an inner surface of the housing by structure for adjoining. The structure for adjoining may comprise a conductance limiting seal. A tray which separates a reticle zone from an optics zone is provided with an aperture.
A drawback of the photolithographic apparatus known from this prior art document is that it has relatively long downtime because, when the vacuum is reduced a relatively long period of time may be required to pump the vacuum chamber back to the vacuum level when operating the photolithographic apparatus.